title: Strong magnetism observed in carbon nanoparticles produced by the laser vaporization of a carbon pellet in hydrogen-containing Ar balance gas.
abstract: Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powder at 1000 °C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet, while the sample prepared in 100% of Ar does not show such magnetism. The observed magnetism was unchanged over months in the ambient. The structure of this nanomaterial resembles the foam of a laundry detergent and transmission electron microscopy indicates a clear corrugated line contrast. On the other hand, a sample without strong magnetism does not give such an image contrast. The x-ray diffraction pattern coincides with that of graphite and no other peak is detected. Thermogravimetry indicates that all samples completely burn out up to approx. 820 °C and no material remains after combustion, indicating that the sample does not contain impurity metals. Magnetization is easily saturated by ∼10,000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon is explained by introducing a crystalline anisotropy which restricts the motion of the magnetic moment and stabilizes the remnant magnetization at zero magnetic field. Magnitudes of the saturation magnetization are in the range of 1-5 emu G g(-1) at 4.2 K, which correspond to 0.002-0.01 Bohr magneton per carbon atom. This concentration may be increased by ten times or more, because only about 4-10% of particles have a magnetic domain in the present samples.
authors.affiliation: Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku, Nagoya 468-8502, Japan.
authors.forename: Hirohito
authors.initials: H
authors.lastname: Asano
authors.forename: Susumu
authors.initials: S
authors.lastname: Muraki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Endo
authors.forename: Shunji
authors.initials: S
authors.lastname: Bandow
authors.forename: Sumio
authors.initials: S
authors.lastname: Iijima
mesh_terms: D001128:Argon / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D007834:Lasers; D008280:Magnetics; D008422:Materials Testing; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000528:radiation effects* / Q000648:ultrastructure
chemical_list: D005740:Gases; D037742:Nanotubes, Carbon; D001128:Argon; D006859:Hydrogen